1. Field of the Invention
This invention relates to an electrophotographic image forming apparatus for forming an electrostatic latent image on an electrophotographic photosensitive member by the electrophotographic method, and visualizing this electrostatic latent image by a developer contained in the developer container of a developing device, and particularly to an electrophotographic image forming apparatus having a developer remaining amount detecting device for detecting the remaining amount of developer contained in a developer container, and further to a process cartridge.
Here, the term xe2x80x9celectrophotographic image forming apparatusxe2x80x9d covers, for example, an electrophotographic copier, an electrophotographic printer (such as an LED printer or a laser beam printer), an electrophotographic facsimile apparatus and an electrophotographic word processor.
Also, the term xe2x80x9cprocess cartridgexe2x80x9d refers to at least one of charging means, developing means and cleaning means and an electrophotographic photosensitive member integrally made into a cartridge that is detachably mountable to the main body of an electrophotographic image forming apparatus, or at least developing means and an electrophotographic photosensitive member integrally made into a cartridge that is detachably mountable to the main body of an electrophotographic image forming apparatus.
2. Related Background Art
An electrophotographic image forming apparatus, such as a laser beam printer, applies a laser beam, corresponding to image information, to an electrophotographic photosensitive member to thereby form a latent image thereon, supplies a developer (toner) as a recording agent to this latent image by developing means to thereby visualize the latent image as a toner image, and further transfers this toner image from the electrophotographic photosensitive member to a recording sheet, which is a recording medium, to thereby form an image.
A toner containing portion, which is a developer container containing the toner therein, is connected to the developing means, and the toner in the toner containing portion is consumed by the image being formed. The toner containing portion, the developing means, the electrophotographic photosensitive member, etc., are often integrally made into a process cartridge, and when the toner is depleted, a user can again form an image by exchanging the process cartridge.
There is an apparatus provided with a construction for outputting an indication to the user so as to prepare the next process cartridge before the toner in the process cartridge is depleted and the quality of the image is reduced. Such an apparatus measures the amount of toner in the toner containing portion of the process cartridge.
A plane antenna is conceived as an example of means for measuring the amount of toner, i.e., developer amount measuring means. The plane antenna comprises a pair of electrodes juxtaposed at a predetermined interval on a substrate, and it is conceived to dispose it in the toner containing portion of the process cartridge along a direction in which the amount of toner changes.
When the toner in the toner containing portion contacts with this plane antenna and the amount of toner is great and the area of contact thereof with the plane antenna is large, the capacitance between the electrodes of the plane antenna is high, and when the amount of toner becomes small and the area of contact thereof with the plane antenna becomes small, the capacitance between the electrodes becomes low. Accordingly, by measuring the capacitance of the plane antenna, it is possible to successively know the amount of toner in the toner containing portion.
Now, as regards the process cartridge, there are sometimes prepared process cartridges mountable on the main body of the same apparatus but differing in the initial fill amount of toner so that a user can select the appropriate cartridge. They include, for example, a 6K cartridge capable of forming standard images on 6,000 sheets, and a 10K cartridge capable of forming standard images on 10,000 sheets.
However, in a case where as a method of indicating the amount of toner, a percentage of the amount of toner at a maximum is indicated as 00%, if the same cartridges differ in the maximum amount of toner they can hold, i.e., the initial fill amount of toner at the start of use, from each other, the area of contact of the toner with the plane antenna will differ. Therefore, a plane antenna of the same construction will become incapable of effecting accurate indication. In the above-mentioned example, if a plane antenna by which the amount of toner at a maximum is indicated as 100% in a 10K cartridge is used for the 6K cartridge, the capacitance of the plane antenna in the 10K cartridge is 60 pF for the maximum amount of toner, as shown in the graph of FIG. 9 of the accompanying drawings. In contrast, in the 6K cartridge, the capacitance is 40 pF. Thus, as shown in the graph of FIG. 10 of the accompanying drawings, in the 6K cartridge, the maximum amount of toner is indicated as 60%.
So, it is conceived to make the design such that even for process cartridges identical in construction with each other but differing in the maximum amount of toner from each other, the amount of toner in the process cartridge can be successively indicated accurately without means for discriminating the difference in the initial fill amount between the cartridges being provided on the main body of the apparatus.
It is an object of the present invention to provide a process cartridge and an electrophotographic image forming apparatus in which even for process cartridges identical in construction with each other but differing from each other in the maximum amount of developer, the amount of developer in the process cartridge can be successively indicated accurately.
It is another object of the present invention to provide a process cartridge in which the pair of electrodes of planar developer amount measuring means are constructed in different patterns in conformity with the initial fill developer amount in a developer container, and an electrophotographic image forming apparatus on which such process cartridge is detachably mountable.
These and other objects, features and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.